I think the main problem with snipers is body shots. They do way too much damage IMO. Don't get me wrong, if someone is a skilled sniper and repeatedly domes me, I don't get annoyed and usually I'll commend their skill. But if someone just double taps me from across the map or finishes me off with a body shot after I've been tickled by someone else's primary, I don't think that's got any skill in it. Despite being a long range precision weapon, its easily viable to bodyshot someone at close range, Quickdraw switch to primary and finish them off.
Another problem is that lag benefits snipers more than any other weapon. Being sniped behind a wall is just unfair. I expect this should be fixed when they make laggers get the disadvantage.
As for aiming under fire, I don't know. I've tried sniping people while under fire and its almost impossible for me. So when people do manage it on me, I just shrug it off as skill or luck. Of course body shotting under fire is much easier which leads me back to my first paragraph.
